Combine all the sauce ingredients in a bowl and stir until smooth.
In another bowl, gently mix together the cornstarch, flour, egg whites, and cold seltzer water to form a tempura batter.
Coat the chicken chunks evenly by dipping them into the batter.
Heat vegetable oil to 350°F to a depth of about 3 inches in a large pot or deep fryer.
Carefully fry the batter-coated chicken pieces in batches until they turn golden and crispy, then drain on paper towels.
Heat sesame oil in a wok or large skillet over medium heat, then sauté the minced garlic and crushed red pepper for about 30 seconds to release their flavors.
Pour the prepared sauce into the skillet and add the fried chicken, tossing quickly to coat everything evenly.
Serve the sesame chicken immediately, garnished with sesame seeds for a crunchy finish.